1. Field of the Invention
The present invention relates to a process for production of a composite part which comprises a component comprising a molding composition based on a higher polyamide.
2. Description of the Related Art
Higher polyamides, in particular those whose monomer units contain an average of at least 8 carbon atoms, have a property profile comprising by way of example impact resistance, low water absorption, chemicals resistance, alcohol resistance, engine-fuel resistance, and solvent resistance. This gives them good suitability for surfaces exposed to environmental effects such as atmospheric moisture or road salt, or exposure to engine fuels, oils, greases, or mixtures with alcohols. Component parts which have to perform a variety of functions are often composed of two or more layers or, respectively, two or more parts, these having been bonded to one another at a bonding surface. The properties of higher polyamide materials often make it advantageous here to form at least one of the layers or, respectively, one of the parts from a molding composition based on a higher polyamide. Typical examples here are items decorated by means of a film or elements of a system that conveys engine fuel or that conveys oil. Component parts of this type are known. For their production, either mutually compatible molding compositions are selected or an adhesion promoter is used. Because the vast majority of plastics are mutually incompatible and therefore do not adhere to one another, an adhesion promoter is mostly used in practice and is usually introduced in the form of a layer. The component part therefore comprises an additional component which in many instances contributes little to the application-related properties demanded from the component part and moreover complicates the production process; by way of example, in the case of the coextrusion process the result here is a requirement for an additional extruder. In the case of multicomponent injection molding, additional injection units are used for each of the components, in combination with mold technology which is often relatively complicated (core-back molds, rotating molds, and indexing plate molds). It would therefore be desirable to obtain successful adhesive bonding between a part comprising a molding composition based on a higher polyamide and a part comprising any desired other molding composition, without any need to use an adhesion promoter.
Current alternative industrial approaches to the problem of chemically/thermodynamically incompatible combinations of materials are based on interlocks, for example undercuts and perforations, or are materials-based, an example being adhesion-modification, or use surface processes such as priming with an adhesion promoter, if appropriate in solution, flame treatment, corona treatment, or low-pressure plasma treatment. However, these solutions are often associated with additional handling cost or increased materials costs. Furthermore, they often do not permit locally limited and flexible surface treatment. Further restrictions become apparent with the bonding of large areas or with processability when by way of example two different materials are processed in the same mold system with different respective ideal mold temperatures.